t.vect.list, t.rast.list: Add CSV support with pipe + skip pytest

[gulshan-123]

This is a followup from #7051

Adds:

1. csv and line format can now use pipe as separator
2. with format=json and yaml if separator is provided, give user error that separator is part of the format
3. Default separator in case of "plain" will be pipe, in case of "line" and "csv" will be comma.
4. skips only tests related to yaml, if yaml is not imported. (Since this is a small change, I included this in the current PR only)

Both t.vect.list and t.rast.list have very similar changes.

---

Skipping yaml test logic in case of parameter is taken from Gemini:

@pytest.mark.parametrize(
    "output_format",
    [
        "json",
        pytest.param(
            "yaml",
            marks=pytest.mark.skipif(
                yaml is None, reason="PyYAML package not available"
            ),
        ),
    ],
)

[petrasovaa]

This looks good, thank you!